Skip to main content

Full text of "Handbook Of Chemical Engineering - I"

See other formats


CRUSHING AND GRINDING
195
as thick as the maximum opening of the swinging jaw, as wide as the width of the rectangular opening and of indefinite length.
As the swinging jaw closes, the angle of nip becomes greater and the tendency is more and more to push the rock out of the machine, rather than to crush it. This is particularly noticeable on rocks of a slippery nature and in any machine where the limit of the angle of nip has been closely approximated by the manufacturer, which is nearly always the case.
Breakers of this type are accomplishing useful work during only half the time they are in operation, the other half being occupied in retreating the moving jaw and getting ready for another compressing operation. Consequently, the proportion of power applied to overcoming friction is high. The product of such machines is not desirable if uniform material is required and its use is only permissible when a machine of a different type is used for secondary crushing, or under special conditions where
FIG. 3.—Gyratory breaker.
uniformity of product is not required. These machines are widely used in spite of their manifest disadvantages because of their comparatively large capacity and low installation cost.
The Dodge type of jaw breaker embodies the same principles as those of the Blake type. The essential difference between the two is that in the Dodge type the movable jaw is hinged at the bottom instead of the top. Its mechanics are illustrated in the accompanying illustration. The result of using a movable jaw, hinged at the bottom, is that the discharge opening is much more nearly constant so that a product more uniform in size character is obtained. It still maintains the disadvantage of delivering a slabby or tabular product. The closing of the movable jaw lessens the angle of nip, thus tending to wedge the rock more tightly between the jaws and to accom-